1. Field of the Invention
The present invention relates to an apparatus and a method for transmitting digital data at high speed over a transmission channel, and preferably for writing to a hard disk drive at high operating speeds.
2. Description of the Related Art
A hard disk drive uses a recording head to receive data from a device that writes, or transmits, the data. Typically, the data propagates from the writer to the head via a transmission line. The data is transmitted in the form of electrical pulses, where each electrical pulses can be characterized by a pulse width which is measured in seconds. The transmission rate of the data is an important circuit characteristic, because a higher transmission rate allows for a larger volume of information to be communicated. Therefore, a common objective of circuit designers is to increase the maximum data transmission rate. Typically, the transmitted pulse is also amplified before it is received. Thus, if there is any signal interference prior to amplification, the received signal may be distorted. Therefore, another common objective of circuit designers is to reduce or eliminate signal interference. Circuitry and transmission lines for providing high-speed communications between writing devices and receiving devices are well known in the art and are the subject of many patents.
In most cases, even when a circuit is designed to operate at a high data transmission rate, the transmission time (i.e., the length of time required for the pulse to propagate from the writer to the head) is greater than the pulse width. In these cases, there are no circuit design considerations relating to intra-pulse characteristics; the pulse is transmitted and received in an intact form. However, when a circuit is being operated at such a high speed that the transmission time is less than (or even nearly equal to) the pulse width, the circuit designer must take several intra-pulse characteristics into account, such as the rise time and fall time of the pulse and the wave propagation characteristics of the transmission line. In particular, if the voltage polarity at the writer (transmitter) changes before the previously transmitted pulse has been received at the head (receiver), then the previously transmitted pulse may be severely distorted before it is received, and the data quality may be degraded. Thus, a dilemma for writing to a hard disk drive via a high speed channel is presented.